Conventional valves are rising or non-rising. In conventional non-rising valves, a valve disk rotates relative to a fixed disk that is urged into contact with the disk by a spring. The use of a spring requires extra inventory and an additional step during the assembly process. A valve assembly that eliminates the spring and the rotating valve disk would provide a material and labor advantage to a manufacturer. In addition to a valve assembly which eliminates the requirement of a spring and rotating valve disk, a valve assembly which offers an alternative to physically or chemically vapor depositing low friction coatings on its sealing components would be desirable.
By way of comparison, U.S. Pat. No. 4,983,355 relates to seal elements formed by compression molding and sintering a powdered hard material and binder composition. The sintered sealing disk can be covered with a thin layer of a silicon carbide, metallic carbide, metallic nitride or carbon having a cubic crystallographic lattice structure applied by physical or chemical vapor deposition. The suggested advantage of this method appears to be a semi-finished product that can be of varying sometimes complicated configurations.
U.S. Pat. No. 4,966,789 relates to a pair of seal members which control the fluid flow of a faucet. The two seals are formed of a moderately hard material such as stellite, ceramic materials, metal materials or synthetic materials which can be precisely ground to a particular finish. At least one of the seal members is coated by either physical or chemical vapor deposition with a thin layer of very hard material such as silicon carbides, metal carbides, metal nitrides or cubic crystallographic lattice carbons. The resulting seal disks are suggested to have low friction coefficients thereby eliminating the need to provide a lubricant between the cooperating surfaces of the disks. In addition, adhesion between the seals is said to be eliminated despite the smooth surface finish of the disks.
Another faucet valve having a specialized sealing disk assembly is disclosed in U.S. Pat. No. 5,100,565. According to this patent, a valve comprising a stationary disk and a rotary disk wherein at least one surface of one of the disks includes a diamond like carbon film is provided. The film comprising diamond like carbon is said to be formed on at least one of the disks by means of a gas phase synthesizing process such as chemical vapor deposition or physical vapor deposition. Hereto the suggested advantage is a valve structure having minimal adhesion between contacting surfaces of the stationary and rotary disks.
While conventional coating processes such as chemical vapor or physical vapor deposition may be employed to coat the valve stem and/or the valve disks of the present invention, it is preferable that a thermal spray process be utilized. Both chemical and physical vapor deposition processes are carried out in a chamber by significantly raising the temperatures within the chamber and creating a vacuum. Because these processes are run at higher temperatures, this limits the substrate materials that can be used. Further, parts can only be produced in batches sized appropriately to the inside treatment chamber. Still another perceived problem is achieving stoichiometric reactions across the entire surface being coated. The chambers must be pumped down, brought to high temperatures for processing and then cooled down before parts can be unloaded from the treatment chamber. This procedure adds considerably to processing time. The coatings generally do not provide the ability to compensate for stamping variations. These processes require multiple chambers to yield the quantities of parts required for valves and are a considerable capital expense and maintenance issue for manufacturing.
According to one aspect of the present invention, a valve assembly employing a valve stem having a sealing surface and a valve disk having a complimentary sealing surface is provided. Preferably, at least one of the surfaces of the valve stem or the valve disk is provided with a low friction material selected from the group consisting of ceramics, cermets, glass and diamond-like carbon, among others. Among the useful ceramics are chromium oxide (chromia), aluminum oxide (alumina), titanium oxide (titania), yttrium oxide (yttria), yttria stabilized zirconia, aluminum titanate, magnesium aluminate (spinel), magnesium zirconate, as well as alloys or blends of these, by way of non-limiting example. Among the useful ceramic metals or “cermets” are tungsten carbide cobalt, tungsten carbide nickel, tungsten cobalt chromium, chromium carbide nickel, chromium carbide nickel chromium, as well as alloys or blends of these, by way of non-limiting example.
A preferred process for providing a coating of a low friction material on the sealing surface of the valve disk and/or the valve stem is by thermal spraying. That is not to say, however, that the valve disk cannot be a sintered ceramic component, for example, formed from a complimentary low friction material is that which is applied to the sealing surface of the valve stem.
By “thermally sprayed” or “thermal spraying”, it is meant that the desired low friction material is applied by either high velocity oxygen fuel spraying, electric arc spraying or plasma spraying. Under a high velocity oxygen fuel technique, a large volume of gas is generated caused by the reaction of fuel gasses with oxygen and formation and thermal expansion of exhaust gases including carbon dioxide and water vapor. These gases exit the chamber through a narrow barrel (e.g., ¼″, {fraction (5/16)}″ diameter) several inches long (e.g., 4″, 6″, 9″). Because of the high pressure created in the combustion chamber, the gases exit the barrel at extreme velocities, thereby accelerating the molten particles. The particles can reach speeds approaching the velocity of the gases, e.g., particle velocities of over 2,500 feet per second have been measured. These high particle speeds and subsequent high kinetic energy, translate into dense coatings with some of the highest bond strengths possible.
The electric arc process involves producing an electric arc between two oppositely charged wires of the same or different metal composition. The wire material is melted between the tips of two charged wires that are fed through the gun. Molten metal produced by the arcing is then atomized by a gas stream and molten droplets are propelled to the part. Electrical power is provided by a power supply similar to that of a typical welding power supplies. Electrical power is delivered at 208/230/460/575 VAC. A common setup in U.S. factories requires 460 VAC at 30 amps delivered to the gun. Output from the gun is typically set for 20-35 volts and 105-300 amps. The wire is fed by electrical pneumatic motors pulling or pushing wire to gun. The wire spool feeders supply wire to the gun through conduits to the tips. Power from the power supply is provided to the gun at the copper contact tubes which are connected to metal tips to transfer electrical power from two contacting wires. Atomization air is typically provided by an air compressor although other gas sources are commonly employed. Typical atomization air is provided at approximately 60-70 cfm and 60-80 psi.
The two-wire arc process is limited to electrically conducting feedstock materials suitable for wire production. Recent developments in wire technology enable producing wires with metallic sheaths that are filled with non-metallic materials (e.g., ceramics, polymers). The two wire arc process can be performed with the wire being the same composition or two different compositions forming a composite coating in-situ. The spray process may be performed at ambient pressure in air, inert atmospheres at atmospheric and low pressure/vacuum conditions. Reactive metals (e.g., titanium) may be sprayed in a variety of gaseous environments to produce either very pure coatings (e.g., with inert gases-argon) or in gaseous environments forming compounds (e.g., TiN) having favorable material properties (i.e., mechanical, aesthetic).
The coatings produced from the electric arc process are a result of the equipment operating parameters, material and process conditions. The arc voltage, amperage, atomization gas (primary, secondary) and pressure may be varied producing a variety of coatings. Material considerations including diameter (e.g., {fraction (1/16)}″, ⅛″, 2 mm) and equipment component designs (e.g., nozzle configurations) control the size of the particle as well as the spray stream pattern. The gun-to-target stand-off distance, traverse rate as well as other process variables also significantly influence the resultant coatings.
Under a plasma spraying technique, an inert gas, usually argon with a mixture of hydrogen or nitrogen, flows through the space between the electrodes, where it is ionized to form a plasma. The feedstock powder material is carried in a stream of gas (e.g., argon, air) and injected into the flame either within the nozzle or as it emerges from the outer face of the anode. The flame accelerates the particles and they are melted by its high temperature, probably supplemented by heat given off as ions recombine and molecules re-associate on the surface of the particles. The molten droplets are propelled onto the target surface, where they solidify and accumulate to form a coating.
Particles are deposited at a rate estimated at roughly a million per second, accumulating into a coating at a rate that depends on the area to be covered and how fast the gun moves over the surface. Each particle solidifies on the order of a millionth of a second, from the orientation of the grains and the overall shape of the splats. As the impacting droplet flattens out on the surface, the substrate acts as a heat sink and a solidification front moves upward through the splat. Certain coatings form chemical bonds with their substrates and metallic coatings can establish a bond as the heat of plasma spraying (the workpiece can reach 200° C. unless it is cooled with jets of air) enables atoms of the coating and the substrate to interdiffuse. A preferred plasma spray apparatus is known under the tradename ELECTROCOTE MODEL 2500.
A preferred coating is formed wherein a series of overlapping sprays form a lamella or layered structure on the substrate. By applying the thermal spray to form a series of overlapping lamella, the overall porosity of layered structure can be maintained below about 5% which is sufficient to retain valve lubricant. The structure does not propagate cracking except locally or on edges, thereby providing a robust sealing surface compared to solid sintered ceramic that can propagate a crack and possibly chip or break into pieces. The thermal spray process can be performed outside of a chamber at atmospheric conditions thereby allowing more freedom of motion for application and unlimited part processing configurations. The coating produced by the thermal spray process can be readily applied in layers such that the final average thickness after lapping, if necessary, is between about 0.003 inches to about 0.008 inches, thereby allowing more flatness variation in a stamped substrate.
According to the present invention, a preferred valve assembly comprises a valve stem having a sealing surface, an annular bonnet configured to receive the valve stem, a valve disk having a sealing surface, a sealing disk and an insert, whereby at least one of the sealing surfaces includes a low friction sealing material. The sealing disk and valve disk are generally arranged in a stacked configuration and are disposed within a recess contained on the insert.
According to another aspect of the invention, a thermal spray process for applying sealing material to the sealing surface of the valve disk and/or the valve stem is disclosed.
According to another aspect of the invention, the valve disk and sealing disk are bow tie shaped and define a first pair of orifices for the passage of fluid therethrough. The sealing disk in particular provides both a sealing function and a biasing function.
According to another aspect of the invention, the valve assembly further includes means for changing the operation between a clockwise and a counterclockwise motion. The bonnet includes four legs that depend downwardly therefrom and the insert includes four projections. The legs are disposed between the projections in a first configuration wherein the valve opens with a clockwise movement. If the bonnet is disengaged from the projections, rotated 90° in either direction relative to the insert and re-engaged with the projections, the valve opens with a counterclockwise movement. Thus any valve manufactured with this feature can be used for knobs or levers without regard to handing. In addition, this feature eliminates the need for the adapters used in conventional valves.
Other features and advantages of the invention will become apparent from the following portion of this specification and from the accompanying drawings, which illustrate a presently preferred embodiment incorporating the principles of the invention.